Pertussis, also known as whooping cough, is a highly contagious respiratory tract infection caused by the bacterium Bordetella pertussis. This disease has been present throughout history, with documented outbreaks dating back to the 16th century. However, it was only in 1906 that Jules Bordet and Octave Gengou discovered the specific bacterium responsible for pertussis.
Transmission of pertussis primarily occurs through respiratory droplets when an infected individual coughs or sneezes. Others in close proximity can inhale the bacteria, leading to infection. Pertussis is highly infectious, with an estimated reproduction number (R0) of 12-17, meaning each infected individual can transmit the disease to 12-17 susceptible individuals.
Although pertussis can affect individuals of all ages, it is most severe in infants under one year old. Infants are especially vulnerable because they have not completed the full series of vaccinations. Pertussis can cause severe coughing fits, difficulty breathing, and in some cases, life-threatening complications. Older children and adults can also contract pertussis, but their symptoms are generally milder and may resemble a prolonged cough.
Globally, pertussis remains a significant public health concern. According to the World Health Organization (WHO), an estimated 24.1 million cases of pertussis occurred worldwide in 2019, resulting in approximately 160,700 deaths. However, these figures may be underestimated due to underreporting and limited resources for accurate diagnosis in many regions.
The burden of pertussis varies among different regions and populations. In high-income countries with robust immunization programs, the incidence of pertussis has significantly decreased. However, occasional outbreaks still occur, primarily affecting unvaccinated or incompletely vaccinated individuals and those with waning immunity. In low- and middle-income countries, pertussis remains a major cause of morbidity and mortality, especially in infants.
There are several risk factors associated with pertussis transmission:
1. Lack of Vaccination: Individuals who are unvaccinated or have not completed the recommended immunization schedule are at a higher risk of contracting pertussis.
2. Waning Immunity: Over time, the protection provided by the pertussis vaccine diminishes, making previously vaccinated individuals susceptible to infection.
3. Close Contact: Being in close proximity to an infected person, particularly in crowded settings like households, schools, or childcare facilities, increases the likelihood of transmission.
4. Age: Infants, especially those under six months old, face the highest risk of severe disease and complications. Adolescents and adults can also transmit the infection to vulnerable populations.
5. Maternal Transmission: Mothers with pertussis can transmit the infection to their newborns. Vaccination during pregnancy (preferably between the 27th and 36th weeks) can offer some protection to the newborn.
The impact of pertussis varies across regions and populations. In high-income countries, where vaccination coverage is high, pertussis rates have significantly declined compared to the pre-vaccine era. However, occasional outbreaks occur due to waning immunity or vaccine hesitancy. In low- and middle-income countries, pertussis remains a major public health issue, contributing to high infant mortality rates. Limited access to healthcare, inadequate immunization coverage, and challenges in diagnosis and treatment all contribute to the persistence of pertussis in these regions.
In conclusion, pertussis is a highly contagious respiratory tract infection caused by the bacterium Bordetella pertussis. It has a global prevalence, with millions of cases reported annually. Pertussis primarily affects infants, but individuals of all ages can be affected. Risk factors for pertussis transmission include lack of vaccination, waning immunity, close contact with infected individuals, and age. The impact of pertussis varies across regions, with higher-income countries experiencing lower prevalence rates compared to lower-income countries, where pertussis remains a substantial burden. Vaccination coverage and public health measures play a crucial role in reducing the transmission and impact of pertussis.

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Seasonal Patterns:
Based on the provided data, there is a clear seasonal pattern in the number of Pertussis cases in mainland China. The number of cases is higher during July and August and lower during January and February. However, there are fluctuations within each year, with peak periods occurring at different months. Overall, there is a consistent pattern of higher cases in the summer and lower cases in the winter.
Peak and Trough Periods:
Pertussis cases in mainland China peak in July and August, with a high number of cases reported during these months. On the other hand, trough periods, or periods with a lower number of cases, are seen in January and February. However, it is important to note that there are fluctuations within each year, and peak periods can occur in different months depending on the year.
Overall Trends:
The overall trend for Pertussis cases in mainland China shows fluctuations over the years, but there is a general increase in cases from 2010 to 2023. The number of cases starts relatively low in 2010, gradually increases until around 2014, and remains at a high level until 2019. There is a decline in cases in 2020, likely influenced by the COVID-19 pandemic, followed by an increase in 2021 and 2022. The highest number of cases is reported in July 2023.
Discussion:
The seasonal pattern of Pertussis cases in mainland China, with peak periods in the summer and lower periods in the winter, aligns with previous research on the disease's seasonality. This pattern is likely influenced by factors such as increased social interactions and more favorable environmental conditions for transmission during the summer. The observed fluctuations within each year could be influenced by various factors, including changes in population immunity, vaccination coverage, and other social and environmental factors.
The overall increasing trend of Pertussis cases in mainland China from 2010 to 2023 underscores the need for continuous monitoring and preventive measures to control the disease's spread. The decline in cases in 2020, coinciding with the COVID-19 pandemic, could be attributed to the implementation of control measures such as social distancing and mask-wearing, which may have inadvertently reduced the spread of Pertussis as well. The increase in cases in subsequent years highlights the potential for resurgences of the disease and emphasizes the importance of maintaining high vaccination coverage and implementing public health interventions to mitigate its impact.